Zur Kenntnis der RbNiCrF6Typs. III. Neue Fluoride des Typs CsZnMF6 mit M = Al,Ga, In,Tl, Sc,Ti, V,Mn, Cu,Rh

On the RbNiCrF₆ Type. III. New Fluorides of the Type CsZnMF₆ (M = Al, Ga, In, Tl, Sc, Ti, V, Mn, Cu, Rh) Cubic compounds are CsZnGaF₆ [3] (colourless, a = 10.29 Å); CsZnInF₆ (colourless, a = 10.58 Å); CsZnTlF₆ (colourless, a = 10.62 Å); CsZnScF₆ (colourless, a = 10.58 Å); CsZnTiF₆ (lightblue, a = 10.50 Å); CsZnVF₆ (lightgreen, a = 10.43 Å); CsZnMnF₆ (redbrown, a = 10.40 Å); CsZnCuF₆ (light brown, a = 10.24 Å); CsZnRhF₆ (redbrown, a = 10.41 Å), all RbNiCrF₆ type of structure, in addition non cubic: CsZnAlF₆ (colourless). The Madelung part of lattice energy, MAPLE, is calculated and discussed.     

Enantioselective synthesis of ferrocenyl nucleoside analogues with apoptosis-inducing activity

[reaction: see text] As a contribution to bioorganometallic chemistry, an enantioselective synthesis of novel carbocyclic nucleoside analogues with a ferroceno-cyclopentene backbone was developed. Diastereoselective cuprate 1,4-addition or Mukaiyama-Michael addition to a planar-chiral enoate (ethyl (E)-2-[2-methoxycarbonyl-ferrocenyl]-acrylate) allowed for the introduction of different side chains (RCH(2)). Other important steps include a Dieckmann cyclization and the attachment of the nucleobase (NB) in an iron-assisted S(N)1 reaction. Some of the target compounds were shown to exhibit significant apoptosis-inducing activity (LD(50) = 10-20 microM) against tumor cells.     

Absolute infrared intensities of hydrocarbons

Dipole-moment derivatives, calculated by both the CNDO/2 method with different parameterizations and the INDO method, are compared to the experimental values determined from absolute infrared intensity measurements for the IR active modes of methane, ethane, ethylene and acetylene. A parameter refinement procedure is introduced in which the CNDO/2 molecular orbital parameters are adjusted through a damped least-squares treatment to give best agreement with the observed dipole-moment derivatives. It is found that the refinement does not substantially improve the agreement obtained with the original CNDO/2 parameterization. The INDO method gives somewhat poorer agreement than the CNDO/2 calculations. As an example of the applicability of the molecular orbital methods toward reproducing relative infrared intensities, the spectrum of cyclopropane in the gasphase is examined.

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Zusammenfassung Die Ableitungen des Dipol-Moments, die nach der CNDO/2-Methode mit verschiedenen Parametrisierungen sowie der INDO-Methode berechnet wurden, werden mit den experimentellen Ergebnissen aus Messungen der absoluten Infrarot-Intensitäten für die IR-aktiven Schwingungen von Methan, Äthan, Äthylen und Azetylen verglichen. Die CNDO/2-Parameter werden mit einer Methode der kleinsten Quadrate den beobachteten Dipol-Moment-Ableitungen angepaßt. Die Ergebnisse sind jedoch nicht wesentlich von denen der ursprünglichen CNDO/2-Methode verschieden. Die INDO-Ergebnisse sind nicht so gut wie die CNDO/2-Ergebnisse. Als Beispiel der Anwendbarkeit der MO-Methoden zur Berechnung von relativen IR-Intensitäten wird das Spektrum des Cyclopropans in der Gasphase untersucht.

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Résumé Les dérivées du moment dipolaire, calculées par la méthode CNDO/2 avec différentes paramétrisations et par la méthode INDO, sont comparées aux valeurs expérimentales déterminées à partir de mesures d'intensité absolue pour les modes actifs dans l'infra-rouge dans le méthane, l'éthane, l'éthylène et l'acétylène. Les paramètres sont ajustés de manière à donner le meilleur accord avec les dérivées du moment dipolaire. Cet ajustement n'améliore pas sensiblement l'accord obtenu avec la paramétrisation CNDO/2 originale. La méthode INDO donne des résultats moins bons que les calculs CNDO/2. Le spectre du cyclopropane en phase gazeuse est étudié comme exemple de l'applicabilité de la méthode des orbitales moléculaires au calcul des intensités relatives infra-rouge.

     

Conjugate additions of a simple monosilylcopper reagent with use of the CuI.DMS complex: stereoselectivities and a dramatic impact by DMS

Conjugate additions utilizing the simple monosilylcuprate reagent Li[PhMe2SiCuI] to alpha,beta-unsaturated carbonyl compounds are described. The presence of dimethyl sulfide (DMS), either as a component originating from the (CuI)4(DMS)3 complex or as a solvent added, has an amazing influence on both chemical yield and the level of diastereomeric ratio (dr) of the products. Gilman-type silylcyanocuprates {Li(Ph2MeSi)2Cu/LiCN} have previously been used to guarantee good results in conjugate addition reactions. External additives such as HMPA, tributylphosphine, or dialkylzinc are not necessary in conjunction with the simple Li[PhMe2SiCuI] reagent. It is demonstrated that the monosilylcuprate reagent with DMS as the solvent is very useful with sterically hindered (beta,beta-disubstituted) enones, and provides very high yields of the beta-silylated 1,4-addition products. Since there is no oligomerization problem associated with the simple monosilylcuprate reagent, this reagent should be considered as a very useful 1,4-silyl donor to enals, enones, and enoates in conjugate addition reactions.     

Studies in mass spectrometry—XV: Retro-diels-alder fragmentation and double hydrogen migration in some polycyclic diketones

In contrast to adducts I of bi-1-cycloalken-1-yls and p-benzoquinone, their reduction products II do not exhibit a double hydrogen migration from δ positions accompanying a ‘retro-Diels-Alder’ type fragmentation. An ordinary retro-Diels-Alder fragmentation was found to take place, with charge retention in the diene portion of the molecule. A double hydrogen migration has been detected in II leading to m/e 112 ion c₂, which differed, however, from that in I in charge retention and in the origin of the migrating hydrogen atoms. Adducts III of di-1-cycloalken-1-yls and naphthoquinone behave similarly to II. They exhibit relatively low abundance ions a, however, due to a double hydrogen migration from δ positions, similarly to I. The origin of the migrating hydrogen atoms have been determined by deuterium labelling. Mechanistic suggestions are presented to explain the observed facts.     

De novo design of synthetic di-iron(I) complexes as structural models of the reduced form of iron-iron hydrogenase

Simple synthetic di-iron dithiolate complexes provide good models of the composition of the active site of the iron-iron hydrogenase enzymes. However, the formally Fe(I)Fe(I) complexes synthesized to date fail to reproduce the precise orientation of the diatomic ligands about the iron centers that is observed in the molecular structure of the reduced form of the enzyme active site. This structural difference is often used to explain the fact that the synthetic di-iron complexes are generally poor catalysts when compared to the enzyme. Herein, density functional theory computations are used for the rational design of synthetic complexes as structural models of the reduced form of the enzyme active site. These computations suggest several possible synthetic targets. The synthesis of complexes containing five-atom S-to-S linkers of the form S(CH2)2X(CH2)2S (X = CH2, NH, or O) or pendant functionalities attached to the three-carbon framework is one method. Another approach is the synthesis of asymmetrically substituted complexes, in which one iron center has strongly electron donating ligands and the adjacent iron center has strongly electron accepting ligands. The combination of a sterically demanding S-to-S linker and asymmetric substitution of the CO ligands is predicted to be a particularly effective synthetic target.     

Structure and ion exchange properties of a new cobalt borate with a tunnel structure "templated" by Na+

The new anhydrous borate Na2Co2B12O21 has been synthesized by flux methods and studied by single-crystal X-ray diffraction (space group I2/a with a = 17.1447(15) A, b = 4.5530(5) A, c = 19.4408(15) A, beta = 103.212(5) degrees , V = 1477.4(2) A3, Z = 4). Refinement of its structure reveals it is the first metaborate exhibiting a tunnel network, with internal dimensions of 4.5 x 8.8 A2. Further single-crystal diffraction studies show that the Na+ ions within the tunnels are exchangeable with Li+ along with the absorption of water molecules to form Li2(H2O)2Co2B12O21, making this compound a unique non-siliceous zeotype.     

A mean-field theory for self-propelled particles interacting by velocity alignment mechanisms

A mean-field approach (MFA) is proposed for the analysis of orientational order in a two-dimensional system of stochastic self-propelled particles interacting by local velocity alignment mechanism. The treatment is applied to the cases of ferromagnetic (F) and liquid-crystal (LC) alignment. In both cases, MFA yields a second order phase transition for a critical noise strength and a scaling exponent of 1/2 for the respective order parameters. We find that the critical noise amplitude η_c at which orientational order emerges in the LC case is smaller than in the F-alignment case, i.e. η^LC_C<η^F_C. A comparison with simulations of individual-based models with F- resp. LC-alignment shows that the predictions about the critical behavior and the qualitative relation between the respective critical noise amplitudes are correct.